JP2000052662A - Reversible thermal recording material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reversible thermal recording material, in which the erasion and display of a visible image can be surely performed even at the instant heating per dot unit with a thermal head, and the erasability within a predetermined temperature range is stable over a long term. SOLUTION: In a reversible thermal recording material, in which a visible image can be displayed and erased by reversibly charging the transparency of a compound, which is produced by dispersingly compounding a crystalline organic low-molecular compound with a resin matrix such as a vinyl chloride- vinyl acetate copolymer, by means of temperature, the reversible heat sensitive recording employs 15-30 wt.% of a polyester resin having the coagulation point of 30 deg.C or below such as a polyester adipate, a polyester phthalate or the like is compounded as the resin matrix and an organic low-molecular compound including a 12C or more fatty acid alkyl ester and a 10C or more aliphatic dibasic acid as an organic low-molecular compound.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reversible thermosensitive recording material capable of displaying and erasing a visible image according to temperature, and more particularly to a commuter pass, an admission permit, cards such as various prepaid cards, OHP sheets and the like. The present invention relates to a reversible thermosensitive recording material that can be used.

[0002]

2. Description of the Related Art In general, a commuter pass used by a user of a transportation system, an admission permit to an event hall or a predetermined building, and other repeatedly used cards are written on the surface by characters such as characters printed by an administrator. The device is checked with the naked eye or magnetically recorded information recorded on cards is read by a device to prevent unauthorized use.

However, if the contents written on the surface of the cards do not match the magnetically recorded information, the administrator cannot immediately judge the correctness of the information only on the front surface, and the reading device of the magnetic recording is erroneous. In some cases, it was difficult to completely prevent unauthorized use of cards and the like.

[0004] Further, even with a magnetic recording card such as a prepaid card or an IC card provided with an IC chip, information recorded on the card, such as a past payment amount or a balance, cannot be visually confirmed every time the card is used. Therefore, both the administrator and the user were inconvenient.

In order to eliminate such inconvenience, a card-type recording apparatus that displays visually recognizable recording information by a reversible thermosensitive recording layer (Japanese Patent Laid-Open No. 54-19377,
JP-A-55-154198) is known.

In this apparatus, a recording material in which a crystalline organic low-molecular substance is dispersed in a polymer resin base material is provided in a layer form,
The step of heating the recording material to a specific temperature area (T1) to make it transparent and the step of heating the recording material to an area (T2) above the specific temperature area to make it cloudy are selectively used to form a layered recording material. It has a mechanism of displaying or erasing a visible image by causing a difference in contrast at a key point.

[0007]

However, the above-mentioned conventional reversible thermosensitive recording material has a narrow temperature region where transparency is high, that is, a temperature region where a visible image can be erased. It is difficult to control the temperature.

That is, the conventional reversible thermosensitive recording material is as follows:
It is possible to erase images with a heating stamp or heating bar that heats a large area with a large amount of heat.However, in particular, instantaneous heating using a thermal head increases the temperature distribution in the thickness direction of the recording layer. It was difficult to completely erase.

As a prior art which addresses the above problem by expanding the transparent temperature range, there is disclosed a reversible thermosensitive recording material in which a higher fatty acid and an aliphatic saturated dicarboxylic acid are dispersed (Japanese Unexamined Patent Publication No.
No. 1363) is known, but even with such a technique, a visible image cannot be reliably erased by instantaneous heat treatment.

In addition, the conventional reversible thermosensitive recording material has a problem that a stable erasing function is not maintained for a long period of time because a temperature region having high transparency (visible light transmittance) moves with time. There was also.

An object of the present invention is to solve the above-mentioned problems and to sufficiently expand a temperature region showing high transparency in a reversible thermosensitive recording material. It is an object of the present invention to provide a reversible thermosensitive recording material that can reliably erase and display a visible image even when heated instantaneously in units.

Another object of the present invention is to provide a reversible thermosensitive recording material in which a highly transparent temperature region is prevented from moving with time, and the erasability in a predetermined temperature region is stable for a long period of time. That is.

[0013]

In order to solve the above-mentioned problems, the present invention comprises mixing a crystalline organic low-molecular compound in a dispersed state with a resin base material and changing the transparency reversibly with temperature. In a reversible thermosensitive recording material capable of displaying and erasing a visible image, a polyester resin was blended with the resin base material.

In the above-mentioned reversible thermosensitive recording material, it is preferable that the polyester resin is a polyester resin having a freezing point of 30 ° C. or less, and its blending ratio is 15 to 30% by weight.

[0015] In order to solve the above-mentioned problems, in the reversible thermosensitive recording material, the crystalline organic low-molecular-weight compound comprises an alkyl ester of a fatty acid having 12 or more carbon atoms and an aliphatic dibasic acid having 10 or more carbon atoms. Thus, a reversible thermosensitive recording material which is an organic low molecular weight compound was used.

The mechanism for estimating the recording / erasing of the reversible thermosensitive recording material according to the present invention will be briefly described below.

In the graph of FIG. 3, schematic diagrams (a) to (g) of the crystal phase dispersed in the resin base material are additionally shown. In the reversible thermosensitive recording material in the state shown in (a) in the figure, the hard resin base material and the crystal (dispersed phase) of the organic low-molecular compound are in close contact with each other at room temperature, and the refractive indices of both are in contact. Is in a transparent state because When heated from this transparent state, both the crystal of the dispersed phase and the resin matrix become soft as shown in (b), and when the temperature further rises, the partially melted crystal is dispersed in the resin matrix as shown in (c). In this state, all of them are in the transparent state up to this point.

Then, when the crystal is heated to a temperature exceeding the melting point of the crystal, the dispersed phase becomes completely liquid as shown in (d), and the recording material becomes semi-turbid due to the difference in refractive index between the softened base material and the liquid. State. When the temperature is lowered from this state, the base material resin is gradually cured, but the recording material maintains a semi-turbid state as shown in (e) until the crystallization temperature of the dispersed phase.

When the cooling is further advanced and the temperature falls below the crystallization temperature of the dispersed phase, some small crystals grown on the basis of some seed crystal are formed and the volume of the dispersed phase shrinks. As shown in (f), a void is formed between the and the dispersed phase, and the recording material becomes completely clouded.

When heated again from the cloudy state, (g)
As described above, since the resin base material softens as the temperature rises and gradually fills the gap, the recording material gradually becomes transparent. When the temperature further rises, the crystal partially melts and becomes transparent as shown in (c).

When the recording material in the transparent state (c) is cooled down to room temperature, the softened resin base material adheres to the dispersed phase so that no void is formed at the boundary even if the recording material is subsequently cooled. ) Will return to the transparent state.

In the case of transparency and opacity according to the mechanism described above, the recording material can be made transparent at a lower temperature by lowering the glass transition point (Tg) of the base resin, and the organic material can be made transparent. The lower the melting point of the crystal of the low molecular compound, the more transparent the recording material can be at a lower temperature.

The reversible thermosensitive recording material of the present invention is based on the knowledge of the above-described mechanism of action, and is obtained by blending a polyester resin having a low freezing point of preferably 30 ° C. or less with a resin base material. The glass transition point (Tg) of the resin base material can be lowered to obtain a reversible thermosensitive recording material in which the resin base material is easily softened even with a small applied energy such as a thermal head.

Further, since the polyester resin has a high molecular weight, it is present in a stable mixed state in the resin base material and is difficult to migrate, and has good water resistance and oil resistance. It becomes a reversible thermosensitive recording material with a certain quality.

Furthermore, the combined use of an alkyl ester of a fatty acid having 12 or more carbon atoms having a low melting point and an aliphatic dibasic acid having a carbon number of 10 or more having a high melting point as a crystalline organic low-molecular compound enables a wide dispersion phase. It becomes a reversible thermosensitive recording material having a melting point, and the temperature region with high transparency expands, and the applied energy region necessary for erasing using a thermal head becomes wide.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION The resin constituting the base resin according to the present invention has good transparency, film formability, elasticity and other heat resistance in a high temperature region, durability under repeated heating conditions, and the like. The following are examples of suitable base resin types.

That is, as the base resin species, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinyl acetate-alcohol copolymer, other Examples include vinyl acetate compounds, vinyl chloride copolymers, polyvinylidene chloride, vinylidene chloride copolymers, polyesters, polyamides, polystyrene, polymethyl (meth) acrylate, and copolymers thereof.

Particularly, vinyl chloride-vinyl acetate copolymer, or vinyl chloride-vinyl acetate copolymer and ultraviolet light (UV)
A mixture with a photo-curable resin such as a curable resin or a radiation-curable resin such as an electron beam (EB) curable resin has a high elastic modulus in a high-temperature region, and has a good durability when repeatedly rewritten (displayed / erased). It is.

In the present invention, as the polyester resin to be added to the resin base material, one having a freezing point of 30 ° C. or less as measured according to JIS K0065 is preferably employed. When the solidification point is lower than 30 ° C., the viscosity is large at the time of compounding, and it is difficult to sufficiently mix it with the material. Suitable polyester resins (solidification points are shown in parentheses) to be added to the resin matrix in the present invention include adipic acid polyester (14 to -32 ° C), sebacic polyester (5 ° C), and phthalic polyester. (-10 to -20 ° C) and one or more polyester resins having a low freezing point selected from the group consisting of polyesters of isophthalic acid (-10 to -20 ° C).

Incidentally, a commercially available industrial material called a polyester plasticizer may be employed as such a polyester resin. Such a plasticizer is composed of a dibasic acid such as adipic acid, sebacic acid, and phthalic acid. It is synthesized by polyesterification with a dihydric alcohol such as 1,2-propylene glycol. In this case, a plasticizer having a molecular weight of about 800 to 4000 using a higher alcohol such as a fatty acid having 8 to 10 carbon atoms or octanol as a sealing agent is commercially available as a plasticizer for plastics.

The ratio of the polyester resin to the resin base material is preferably 15 to 30% by weight. This is because if the amount is less than 15% by weight, the erasing characteristics over time cannot be sufficiently maintained, and if the amount exceeds 30% by weight, the contrast of the formed image deteriorates and the visibility decreases. Because.

The crystalline organic low molecular weight compound to be mixed with the resin base material in a dispersed state is preferable because an alkyl ester of a fatty acid having 12 or more carbon atoms has a low melting point (mp). Aliphatic dibasic acids of 10 or more are preferred because of their high melting points (mp).

Examples of the alkyl ester of a fatty acid having 12 or more carbon atoms include fatty acids such as lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, lignoceric acid, serotinic acid, and melicic acid, and methyl, propyl, and so on. Examples thereof include an alkyl ester with an alkyl group such as palmityl, stearyl, and behenyl.

Examples of the aliphatic dibasic acid having 10 or more carbon atoms include suberic acid (mp: 140 ° C.), sebacic acid (m
p: 134 ° C), dodecandioic acid (mp: 128 ° C), tetradecandioic acid (mp: 125 ° C), hexadecandioic acid (mp: 125 ° C), octadecandioic acid (mp: 125 ° C)
° C) and eicosane diacid (mp: 123 ° C).

By appropriately adjusting the mixing ratio of the fatty acid alkyl ester and the aliphatic dibasic acid, it is possible to arbitrarily change the temperature range for transparency, the degree of transparency, and the degree of turbidity in the cloudy state. it can. It is preferable to set the mixing ratio in consideration of the performance of a printing / erasing apparatus that actually uses a reversible thermosensitive recording material, the sharpness of printing contrast, and the like.

An embodiment of a card type recording apparatus using the reversible thermosensitive recording material of the present invention will be described below with reference to the accompanying drawings.

In the card-type recording apparatus shown in FIGS. 1 and 2, a reflection layer 2 made of aluminum or the like for forming an optical reflection surface is provided on the surface of a card base 1 made of a synthetic resin sheet such as polyethylene terephthalate. A recording layer 3 made of the above-described reversible thermosensitive recording material is provided on top of the above, and a protective layer 4 and a printing layer 6 for forming a recording display window 5 are further provided thereon. Has a magnetic recording layer 7 and a protective printing layer 8 sequentially laminated and integrated.

The reflection layer 2 is used to make the image formed on the recording layer 3 easy to see from the surface of the card. Consists of a coating layer of paint.

The recording layer 3 can be formed integrally with the reflection layer 2 by applying a liquid reversible thermosensitive recording material which has been liquefied by adding a solvent, and heating and drying it.

The protective coating layer 4 provided on the recording layer 3 is formed of a transparent resin film having good heat resistance, and specific resin materials include polyethylene terephthalate, polyetherimide, polyetherketone, and polyetherether. Examples thereof include heat-resistant resins such as ketone, polysulfone, polyphenylene sulfide, polyacrylate, polyether sulfone, polycarbonate, polyethylene naphthalate, polyimide, and acrylic resin.

Since the card-shaped recording material formed as described above has a wide temperature range in which the recording layer can be made transparent, an image can be reliably erased by instantaneous heating with a thermal head having a wide temperature distribution. Overwrite that does not require deterioration of the erasability of the recording material due to aging, printing and erasing can be combined with a single thermal head, erasing and reprinting can be performed simultaneously, and initialization by erasing the entire area is not required. Therefore, the speed of the re-recording process can be improved.

[0042]

EXAMPLES AND COMPARATIVE EXAMPLES The raw materials of the reversible thermosensitive recording materials used in the examples and comparative examples are collectively shown below. (1) Vinyl chloride-vinyl acetate copolymer (manufactured by Nissin Chemical Co .: Solvain C) (2) Polyester adipic acid (manufactured by Dainippon Ink Co., Ltd.):
(Polysizer W-4000, freezing point 14 ° C) (3) Polyester phthalate (manufactured by Dainippon Ink and Company: Polysizer P-29, freezing point -10 ° C) (4) Hexadecyl stearate (5) Dodecane diacid
.

Examples 1-4, Comparative Examples 1-3 Aluminum was previously vapor-deposited on the surface of a 188 μm-thick polyethylene terephthalate resin sheet (card substrate) coated with a 10 μm-thick magnetic paint. Was dissolved in tetrahydrofuran, applied to a recording material, and dried by heating to form a recording layer having a thickness of 10 μm.

Then, a protective film made of polyethylene terephthalate resin having a thickness of 2 μm is adhered on the recording layer, and printing for forming a recording display window is performed thereon, and a magnetic recording layer is formed on the back surface of the card base material. Then, a protective printing layer was sequentially superposed, and a card-type reversible thermosensitive recording material in which these were laminated and integrated was prepared.

A printing test was performed on the obtained card-type reversible thermosensitive recording material under the following conditions. That is, the card-type reversible thermosensitive recording material is 0.30 mJ / d.
After printing with a thermal head (white turbid image formation) at ot, for the one immediately after printing and the one left at room temperature for 30 days after printing, 0.01 mJ / dot interval from 0.01 mJ / dot to 0.30 mJ / dot, respectively. And heated to room temperature.

In addition to examining the erasable applied energy range (mJ / dot) in the above state or the above,
Or Macbeth reflection densitometer (RD-914)
And the results are shown in Table 2. Regarding the reflection density, 0.5 or less was evaluated as a cloudy state and 1.0 or more as a transparent (erased) state.

[0047]

[Table 1]

[0048]

[Table 2]

As is clear from the results in Table 2, in Comparative Example 1 in which no polyester was added to the resin base material or in Comparative Example 2 in which the amount of addition was less than the predetermined amount, the erasing characteristics deteriorated after 30 days. In Comparative Example 1, erasing was impossible in an energy application region of 0.01 mJ / dot to 0.30 mJ / dot. In Comparative Example 3 in which the amount of polyester added was too large relative to the resin base material, the contrast of the print (difference in reflection density) was small, and the visibility was reduced.

On the other hand, the solidification point 3
In Examples 1 to 4 in which a predetermined amount of polyester of 0 ° C. or less was added and other conditions were satisfied, the erasing characteristics did not change with time, and the display and erasing of a visible image could be completely performed. Was also good in visibility.

[0051]

As described above, the present invention has a low freezing point of preferably 30 ° C. or less with respect to the resin base material of the reversible thermosensitive recording material in which a crystalline organic low-molecular compound is blended in a dispersed state. By blending the polyester resin, the temperature range showing high transparency can be expanded, and even when a small area of a dot (dot) unit is heated in a short time by the thermal head, the display and erasure of the visible image are completely completed. There is an advantage that can be performed.

Further, such a reversible thermosensitive recording material is
There is also an advantage that the temperature region having high transparency does not move over time, and the reversible thermosensitive recording material has a stable erasing function over a long period of time.

Further, an invention in which a polyester resin is blended in a resin base material of a reversible thermosensitive recording material, and an alkyl ester of a fatty acid having a low melting point and an aliphatic dibasic acid having a high melting point are used in combination as a crystalline organic low molecular weight compound. Thus, the temperature region having high transparency is further expanded, and the reversible thermosensitive recording material can be more reliably erased by the thermal head.

[Brief description of the drawings]

FIG. 1 is a perspective view of a card-type reversible thermosensitive recording material.

FIG. 2 is an enlarged sectional view of the card-type reversible thermosensitive recording material of FIG.

FIG. 3 is an explanatory diagram of a mechanism for estimating recording / erasing of a reversible thermosensitive recording material.

[Description of Signs] 1 Card substrate 2 Reflective layer 3 Recording layer 4 Protective coating layer 5 Recording display window 6 Printing layer 7 Magnetic recording layer 8 Protective printing layer

Claims (5)

[Claims] 1. A reversible thermosensitive thermosensitive element capable of displaying and erasing a visible image by mixing a crystalline organic low-molecular compound in a dispersed state with a resin base material and reversibly changing the transparency of the compound according to temperature. A reversible thermosensitive recording material, wherein a polyester resin is blended in the resin base material. 2. The reversible thermosensitive recording material according to claim 1, wherein the polyester resin is a polyester resin having a freezing point of 30 ° C. or lower. 3. The compounding ratio of the polyester resin is 15 to 15.
The reversible thermosensitive recording material according to claim 1, wherein the content is 30% by weight. 4. The crystalline organic low molecular weight compound has 1 carbon atom.
The reversible thermosensitive recording material according to claim 1, which is a low-molecular organic compound containing an alkyl ester of two or more fatty acids and an aliphatic dibasic acid having 10 or more carbon atoms. 5. The polyester resin according to claim 1, wherein the polyester resin is at least one polyester resin selected from the group consisting of adipic acid polyester, sebacic polyester, phthalic polyester and isophthalic polyester. Reversible thermosensitive recording material.